Axial turbo compressor for a gas turbine having low radial gap losses and diffuser losses

ABSTRACT

An axial turbo-compressor for a gas turbine having a stator vane assembly that is formed by stator vanes having vane tips exposed on the hub side and a stationary shaft cover on the hub side and delimits the flow channel of the axial compressor is provided. A radial gap is designed between the shaft cover and the van tips that is minimally sized such that the axial turbo-compressor may still be assembled, and there is a plurality of recesses in the shaft cover, wherein one of the recesses is allocated to each vane tip that is arranged directly neighboring the vane tip allocated thereto and is sized such that during operation of the axial turbo compressor every vane tip may be plunged into the recess allocated thereto without one of the vane tips significantly contacting the shaft cover.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2010/050933, filed Jan. 27, 2010 and claims the benefitthereof. The International Application claims the benefits of EuropeanPatent Office application No. 09002056.1 EP filed Feb. 13, 2009. All ofthe applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to an axial turbocompressor for a gas turbine,wherein the axial turbocompressor has low radial gap losses.

BACKGROUND OF INVENTION

A gas turbine has a turbocompressor, for example in an axial type ofconstruction. The turbocompressor has a casing with a stator attachedthereupon, and a rotor which is enclosed by the casing. The rotor has ashaft on which the rotor can be rotationally driven. Provision is madefor a shaft cover, encompassing the shaft, the outer contour of whichtogether with the inner contour of the casing form a part of the flowpassage through the turbocompressor. The flow passage has a crosssection which widens in the flow direction so that the flow passage isformed as a diffuser.

The rotor has a multiplicity of rotor stages which are formed in eachcase by a rotor blade row. Also, the stator has a multiplicity of statorblade rows which, as seen in the axial direction, are arranged in amanner in which they alternate with the rotor blade rows. As seen in theflow direction, a guide vane row is customarily arranged after the lastrotor blade row and a downstream guide vane row arranged after that.

The guide vane rows have a multiplicity of vanes which by their one endare fastened in each case on the casing and by their other end pointtowards the shaft. A vane tip, which faces the shaft cover and isarranged directly adjacent thereto, is formed on the other end of theguide vane. The distance between the vane tips and the shaft cover isformed as a radial gap which is dimensioned in such a way that on theone hand the vane tips do not butt against the shaft cover duringoperation of the gas turbine and on the other hand the leakage flowthrough the radial gap which ensues during operation of the gas turbineis as low as possible. This radial gap is therefore to be designed assmall as possible so that high efficiency is achieved and the fullblading potential of the compressor can be exploited. Alternatively tofreestanding compressor vanes, it is also known from EP 1 079 075 A2,for example, to secure the hub-side ends of the vane airfoils, by meansof a locking bolt, against an outwards movement from a hub-side fixedinner ring and to provide damping against vibration occurrences.

The casing of the turbocompressor is solidly constructed in order to beable to withstand the pressure stresses and temperature stresses duringoperation of the gas turbine. Also, the casing is of a rigidconstruction so that load transfer onto the casing during operation ofthe gas turbine results in only minor deformation of the casing. Incontrast to this, the shaft cover is subjected to lower mechanicalstresses during operation of the gas turbine, as a result of which theshaft cover is of a thinner and less solid construction than the casing.

Owing to the fact that the shaft cover is designed with lower wallthicknesses in comparison to the casing and as a rule has differentmaterial properties than the casing, the shaft cover heats up morequickly than the casing with the guide vane rows fastened thereupon.This has the result that for starting and shutting down the gas turbinethe shaft cover and the casing have a different rate of thermalexpansion so that during starting and shutting down of the gas turbinethe depth of the radial gap alters, wherein the radial gap istemporarily smaller during starting and larger during shutting down.

So that the vane tips of the guide vane row do not butt against theshaft cover and damage this during operation of the turbocompressor, theradial gap is provided with a minimum depth which is dimensioned in sucha way that in each operating state of the gas turbine—steady state aswell as transient—the vane tips seldom if ever come into contact withthe shaft cover. This has the result that a correspondingly dimensionedradial gap is provided at the vane tips which leads to a reduction ofthe efficiency of the gas turbine.

Also, the blockage which is created by the radial gap leads to areduction of the main flow components, as a result of which the pressurerecovery in the diffuser is reduced and disadvantageous separationphenomena can occur.

SUMMARY OF INVENTION

It is the object of the invention to create an axial turbocompressor fora gas turbine, which has high efficiency and high operationalreliability.

The axial turbocompressor according to the invention for a gas turbinehas a guide vane cascade, which is formed by guide vanes with vane tipswhich are free standing on the hub side, and a stationary shaft coverwhich is arranged directly adjacent to the vane tips on the hub side anddelimits the flow passage of the axial compressor, wherein between theshaft cover and the vane tips a radial gap is formed and is minimallydimensioned in such a way that the assembly of the axial turbocompressorcan only just be accomplished, and in the shaft cover provision is madefor a multiplicity of blind hole-like recesses, wherein one of therecesses is associated with each vane tip and arranged directly adjacentto the vane tip which is associated therewith, and dimensioned in such away that during operation of the axial turbocompressor each vane tip cansink into its associated recess without one of the vane tips coming intosignificant contact with the shaft cover.

As a result, the radial gap between the vane tip and the shaft cover isadjusted to the minimum required assembly gap so that the depth of theradial gap is reduced to the assembly-dependent minimum. The depth ofthe minimum required assembly gap is selected in such a way that therolling in of the guide vane cascade, especially of the rear guide vanecascade, can be accomplished.

In a conventional turbocompressor, the radial gap between the vane tipsand the shaft cover is provided with a minimum required depth which isselected in such a way that in practically all conceivable operatingstates of the gas turbine the vane tips scarcely come into contact with,or do not make contact with, the shaft cover. Consequently, the radialgap is created with such depth that an appreciable mass flow of leakageflow flows through the radial gap, which leads to an undesirablelowering of efficiency of the gas turbine.

However, in the case of the axial turbocompressor according to theinvention the radial gap is adjusted to the minimum possible radial gap,specifically to the minimum required assembly gap, so that the leakageflow through the radial gap is minimal. As a result, the axialturbocompressor has a high pressure recovery in the diffuser section andtherefore high efficiency.

Also, the vane tips can sink into the recesses during operation of theaxial turbocompressor so that although the radial gap is reduced to theminimum required assembly gap, a damaging contact of the vane tips withthe shaft cover during operation of the axial turbocompressor isprevented.

If the vane tip sinks into its associated recess during a specificoperating state, then the flow around the vane tip decreases, as aresult of which the leakage flow at the vane tip also decreases.Consequently, the efficiency of the guide vane cascade increases andlosses and also separations in the diffuser which lies downstream of theaxial turbocompressor are reduced. In all, a good overall machineperformance and high overall machine efficiency of the gas turbineresult from the improved radial gap behavior. By implication, for thisthe divergence degree of the diffuser, i.e. the diffuser angle of thediffuser, can be selected larger than would be the case with aconventional diffuser. A reduction of the overall length of the gasturbine compared with a conventional gas turbine is associated withthis.

It is preferred that a honeycomb-like and/or felt-like structure, whichcan yield during contact by the vane tip, is applied to the base of therecess. The honeycomb-like structure is preferably a honeycomb.

Consequently, the vane tip can sink into the honeycomb-like and/orfelt-like structure, wherein the vane tip is not damaged. Resulting fromthis is the advantage that the distance between the vane tip and thehoneycomb-like and/or felt-like structure is designed to be small.Therefore, the flow around the vane tip decreases if the vane tip sinksinto its associated recess during a specific operating state and digsinto the honeycomb-like and/or felt-like structure. As a result, theleakage flow at the vane tip advantageously additionally decreases.

Also, it is preferred that the recesses have an outline shape on thesurface of the shaft cover which is adapted to the profile of the guidevanes associated therewith at the vane tip, and have a prespecifieddepth.

Therefore, the material of the shaft cover is arranged in such a wayaround the vane tip which is sunk into the recess that on the one handthe vane tip does not butt against the shaft cover when sinking into therecess and on the other hand the flow around the vane tip decreases.

It is preferred that the depth of the recesses is determined in such away that during operation of the axial turbocompressor the radialrelative movements between the vane tips and the shaft cover can becompensated.

As a result, prevention of a collision of the vane tip with the shaftcover during operation of the axial turbocompressor is advantageouslyachieved, so that the operational reliability of the axialturbocompressor is high.

Moreover, it is preferred that the outline shape of the recesses isdetermined in such a way that during operation of the axialturbocompressor the axial relative movements between the vane tips andthe shaft cover can be compensated.

Therefore, the effect of the vane tips coming into contact with theshaft cover during axial relative movements between the vane tips andthe shaft cover during operation of the axial turbocompressor isprevented, so that the operational reliability of the axialturbocompressor is high.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is shown based on a preferred exemplaryembodiment of an axial turbocompressor according to the invention, withreference to the attached schematic drawings. In the drawing:

FIG. 1 shows a perspective view of a detail of the axialturbocompressor, and

FIG. 2 shows a view along the vane longitudinal axis of the detail fromFIG. 1.

DETAILED DESCRIPTION OF INVENTION

As is evident from FIGS. 1 and 2, an axial turbocompressor 1 has a guidevane cascade 2 which is formed by a multiplicity of guide vanes 3. Theguide vanes 3 are arranged in a row in the circumferential direction ofthe axial turbocompressor 1 and have a longitudinal extent in the radialdirection of the axial turbocompressor 1.

Also, the axial turbocompressor 1 has a casing 5 on which the guidevanes 3 are fastened on the inner side. Facing away from the casing 5,the guide vanes 3 have a vane tip 4 which points inwardly into thecasing 5.

On the hub side, a shaft cover 6, which is designed as acircumferentially symmetrical ring, is arranged directly at the vanetips 3. On the outer side of the shaft cover 6 which faces the vane tips4, provision is made for a multiplicity of recesses 7. Each recess 7 isassociated with a different vane tip 4, wherein the recess 7 is locateddirectly adjacent to its associated guide vane tip 4. The recess 7 isformed like a blind hole and therefore terminates in a blind manner.That is to say, it is provided with a tightly sealed off base in orderto avoid leakage losses.

Each recess 7, on the outer side of the shaft cover 6 facing the vanetips 4, has a contour 8 which is adapted to the profile shape of theguide vane 3 at the guide vane tip 4. Also, each recess 7 is providedwith a depth 9 in the shaft cover 6. The shape of the contour 8 and thedepth 9 are determined in such a way that during operation of the axialturbocompressor each vane tip 4 can sink into its associated recess 7,wherein during the sinking in the vane tip 4 does not come into contact,or barely comes into contact, with the shaft cover 6.

Applied to the base of each recess 7 is a honeycomb structure 10, as isshown in FIG. 1 by way of example for the middle recess 7. If, duringoperation of the axial turbocompressor, the vane tips 4 come intocontact with the honeycomb structure 10, then the honeycomb structure 10yields so that the vane tip 4 presses into the honeycomb structure 10.

1.-5. (canceled)
 6. An axial turbocompressor for a gas turbine, comprising: a guide vane cascade, which is formed by a plurality of guide vanes including a plurality of vane tips which are free standing on a hub side; and a stationary shaft cover, which is arranged directly adjacent to the plurality of vane tips on the hub side and delimits a flow passage of the axial compressor, wherein a radial gap is formed between the shaft cover and the plurality of vane tips and is minimally dimensioned in such a way that an assembly of the axial turbocompressor may only just be accomplished, and provision is made in the shaft cover for a plurality of recesses, and wherein one of the plurality of recesses is associated with each vane tip and is arranged directly adjacent to the vane tip which is associated therewith, and dimensioned in such a way that during operation of the axial turbocompressor each vane tip may sink into the associated recess without one of the plurality of vane tips coming into appreciable contact with the shaft cover.
 7. The axial turbocompressor as claimed in claim 6, wherein a honeycomb-like structure, which may yield during contact by the vane tips, is applied to a base of each recess.
 8. The axial turbocompressor as claimed in claim 6, wherein a felt-like structure, which may yield during contact by the vane tips, is applied to a base of each recess.
 9. The axial turbocompressor as claimed in claim 6, wherein a honeycomb-like and felt-like structure, which may yield during contact by the vane tips, is applied to a base of each recess.
 10. The axial turbocompressor as claimed in claim 6, wherein each recess includes a contour shape on a surface of the shaft cover which is adapted to a profile of the plurality of guide vanes at the vane tip, and includes a prespecified depth.
 11. The axial turbocompressor as claimed in claim 10, wherein the depth of the plurality of recesses is determined in such a way that during operation of the axial turbocompressor the radial relative movements between the plurality of vane tips and the shaft cover may be compensated.
 12. The axial turbocompressor as claimed in claim 10, wherein the contour shape of the plurality of recesses is determined in such a way that during operation of the axial turbocompressor the axial relative movements between the plurality of vane tips and the shaft cover may be compensated. 